Full-speed QUAD-CrossFire

[Banderon]

With the X38 chipset out in the wild, PCIe 2.0 is finally upon us, offering twice the bandwidth of the original PCIe standard. Correct me if I'm wrong, but I've read in a number of threads on this forum that today's PCIe 1.0 x16 vid cards don't really make full use of the 4GB/s bandwidth that the x16 connection allows for. Thus, any current cards released with a PCIe 2.0 x16 interface (for example, cards from the Radeon HD 3800 series) are going to be wasting about half of their 8GB/s maximum bandwidth. Doesn't this mean that running a PCIe 2.0 x16 card at x8 (on a PCIe 2.0 motherboard) should incur barely any performance loss (if any at all)?

Am I correct then in figuring that if we were to hook up say, four PCIe 2.0 x16 vid cards in CrossFire on a Gigabyte GA-MA790FX-DQ6 (4 PCIe 2.0 x16 slots, 2 @ x16 and 2 @ x8), we'd effectively be running a full-speed PCIe 1.0 x16 QUAD-CrossFire system?

 

[Syntax Error]

Are you thinking something like the 7950GX2 and say, two 8800GTs sandwiched into a double slotted, dual PCB card but with only 1 PCI-e 2.0 connector and SLI'ing this "8850GX2" to make it a DIY "quad" SLI?

 

[PCTC2]

no, he's thinking like the new AMD 790FX Chipset on Asus's board is capable of quad PCIe 2.0 8x in PCIe 16x slots. (or really how the concept could be applied to the X38 or 780i)

 

[Banderon]

Yeah, PCTC2, exactly. I'm talking about ATI cards, since those are what the X38 chipset supports. And I mean 4 actual single-slot cards such as the HD 3850 (4 dual-slot 3870 cards would definitely not be able to fit), all connected together in an actual 4-card CrossFire system.

Though, now that I think about it some more, I suppose it wouldn't really be possible since the two x16 channels are connected directly to the X38 chipset, while the rest of the PCIe channels are connected to the southbridge. The north and south only have 2GB/s between them, right? I suppose that'd kinda throw a wrench into the works. Guess we'll have to stick with the 790FX. Though, here is a clear example of why the AMD/ATI merger is bad for consumers. The 790FX is for AMD CPUs, so anyone that was hoping for a Quad-CrossFire system with a Core 2 is out of luck. Before the merger, ATI would have surely wanted both platforms to be able to support quad cards.

 

[soccerballtux]

PCI-e 2 8x = PCI-e 1 16x